1. Field of the Invention
The present invention relates to an electrophotographic color image forming apparatus. More particularly, the present invention relates to a voltage switch of an electrophotographic color image forming apparatus wherein the voltage switch can sequentially apply a development voltage to each color development unit, such that each of the color development units can apply its toner to an electrostatic latent image of a photoconductor for developing the latent image.
2. Description of the Related Art
An electrophotographic image forming apparatus is a device in which an electrostatic latent image is formed on an outer circumference of a photoconductor charged to a predetermined electric potential by scanning light onto the photoconductor. A toner which is a developing agent is applied onto the electrostatic latent image and is developed as a black-and-white or color image, and the image is then transferred and fixed onto a paper so that an image is printed. A typical electrophotographic image forming apparatus capable of color printing includes a light scanning unit for emitting light beams that correspond to an image data, a photoconductor on which the emitted light beams are projected to form an electrostatic latent image, and four development units having yellow (Y), magenta (M), cyan (C), and black (K) toners, respectively, to apply these toners to the electrostatic latent image of the photoconductor for developing the latent image into a visible toner image.
During the developing by the development units, the four kinds of toners can be applied from the development units to the photoconductor by a force resulting from a potential difference between the development units and the photoconductor. To form the potential difference, a high voltage must be applied to the four development units in sequence.
FIG. 1 is a schematic view of a conventional voltage switch of an electrophotographic color image forming apparatus.
Referring to FIG. 1, a voltage switch 10 includes a solenoid 12 and a circuit board 20. The circuit board 20 includes a first terminal 21 connected to a power supply 1 for supplying high voltages up to 3 kV, a second terminal 22 connected to a cyan development unit 5C containing a cyan (C) toner, and a leaf spring 17 having ends 17a and 17b, the end 17a being fixed to the circuit board 20 for an electrical connection with the second terminal 22 and the other end 17b being spaced apart from the first terminal 21 but being capable of contacting the first terminal 21.
The solenoid 12 is securely installed to the circuit board 20 by a bracket 15 and is provided at one end with a holder 13 that is coupled with the end 17b of the leaf spring 17. Though the four development units containing the yellow (Y), magenta (M), cyan (C), and black (K) toners, require four solenoids, only the solenoid 12 for the cyan development unit 5C is illustrated in FIG. 1 as an example, and the remaining solenoids each have substantially the same structure.
When the solenoid 12 of the voltage switch 10 is switched on, the holder 13 coupled with the end 17b, moves toward the first terminal 21 such that the end 17b comes into contact with the first terminal 21. The power supply 1 supplies power to the first terminal 21 such that a development bias voltage is applied to the cyan development unit 5C to cause a potential difference between the cyan development unit 5C and the photoconductor (not shown). The potential difference ensures that the cyan (C) toner can move from the cyan development unit 5C to the photoconductor for developing a cyan (C) toner image. When the solenoid 12 is off and the power supply 1 is off, the developing of the cyan (C) toner image is completed. In the same manner, each solenoid provided for the magenta (M), yellow (Y), and black (K) development units, is sequentially operated to supply power from the power supply 1 to the development units.
However, the voltage switch 10 of the conventional electrophotographic color image forming apparatus is not suitable for a small color image forming apparatus because of its size. Though there are other types of conventional voltage switches using a relay or a solid stator instead of the solenoid, these kinds of voltage switches cannot be used at a high voltage of about 3 kV. Further, conventional voltage switches that can be used at high voltages are too big and expensive to be used in a small-sized, low-priced color image forming apparatus.
Accordingly, a need exists for a system and method for providing a lower cost, smaller sized voltage switch that can operate safely at higher voltages.